Filter



Original Filed June 7, 1943 R. LEPsoE ETAL v FILTER 2 She ets-Sheet 2 :lwenwmg R. Lepsoe E. L. Jones Patented Oct. 5.194s

FILTER Robert Lepsoe and Edward Llewelyn Jones, Trail,

British Columbia, Canada,

orsto'l'he Consolidated Mining and smelting Company of Canada, Limited, Montreal, Quebec, Canada,

a corporation of Canada al application June 7, 1943, Serial No. Divided and this application June 3,

1944, Serial No. 538,608

3 Claims. (Cl. 210-62) This invention relates to a new and useful filter-and is particularly directed to providing an apparatus for effecting the substantially complete removal of iron from crude and refined tin.

This application is a division of our application for Letters Patent of the United States of America No. 489,930, filed June 7, 1943, now abandoned.

Iron is usually present in tin concentrates and is an objectionable impurity throughout tin smelting and refining processes. The iron-tin alloys, in particular, cause considerable difficulty in refining operations. The published literature provides little information on methods'for the elimination of iron from crude and refined tin. The adverse efiect of the presence of even small amounts of iron on the working properties of the refined tin is relatively well known, of course, and a, number of proposals have been suggested for the treatment of the tin concentrates or the crude metal for the recovery therefrom of a refined tin substantially free from iron. Such proposals as are described in thepublished literature on the subject involve relatively costly and complicated operational procedures and result in uneconomical losses of the metal of interest.

It has been found that iron is soluble in tin at high temperatures, for example, a mixture of I iron and tin containing up to about 19% iron is liquid at temperatures above 1100" C. As the temperature is lowered, an iron-tin compound begins to crystallize out of the -moltenmixture. At 500 0., the iron-tin compound has the formula FeSm. The iron continues to crystallize out of the liquid as FeSm until, at temperatures approximating the melting point of tin, 232 0,, substantially all the iron originally contained in the mixture has crystallized in the form of an iron-tin compound, leaving the molten tin substantially free from iron. At temperatures approaching the melting temperature of tin, therefore, only two phases are present in the mixture, solid FeSn: and liquid tin substantially free from iron.

Advantage has been taken of this solubility relationship to provide an apparatus suitable for effecting the substantially complete separation and removal of the iron contained in crude'and refined tin. V V

A principal object of this invention is to provide a filtering apparatus, including a novel arrangement of parts, whereby molten tin passed completely separated from the solid iron-tin compound suspended in the molten tin.

A further object of the invention is to -provide an inexpensively"constructed, easily operated apparatus for effecting the substantially complete separation and removal of the iron content from iron-bearing crude or refined tin.

A filtering apparatus suitable for carrying out the objects of theinvention includes, in general, a cover in communication with a filtrate receiving basing, a filtering medium between the cover and the basin, means for circulating molten tinfrom a holding pot to and through the cover, and means for forcing molten tin through the filtering medium whereby impurities insoluble in the molten tin under the prevailing temperature conditions are carried in suspension in the mol-.

cover, and are retained on the filtering medium, and the molten tin, after passing through the filtering medium, is substantially free from such insoluble impurities.

An understanding of the manner in which the above and other objects of the invention are attained may be had from the following description, reference being made to the accompanying drawings in which:

Figure 1 is a top plan view of a preferred form of filtering apparatus of the present invention;

Figure 2 is a front elevation, in section, of the filtering apparatus;

Figure 3 is a plan view taken along the lines 3---3 of Figure 2;

Figure 4 is a side elevation; and

Figure 5 is an enlarged detail view of the filter features of the present invention comprises, in

general, a .cover i2, a perforated plate II on which is carried a filtering medium l0, and a filtrate receiving basin i l, the structural arrangement of which is described in detail here inafter.

The filtrate receiving basin i4 is preferably of an inverted conical shape and is provided, at

iThe'filtrate receiving basin is supported from the bottom of the basin, with an outlet conduit i5 which extends to a, casting pot (not show).

the floor on columns it, the upper ends of which into and through theappa'ratus is rapidly and 5 The cover I! is preferably of a bell or dome shape, being referred to hereinafter as a filter bell, the base of which is formed with a flange l8 which seats on the flange ll of the filtrate receiving basin I4, being locked in its fixed position on the flange I1 by the eye-bolts 31 which extend through the aligned slots 39. The filter plate II, on which the filtering medium is carried is in the form of a perforated plate which extends between the filter bell and the basin, and is-secured between the flanges I1 and I8, the filtering medium l serving to seal the joints between those flanges.

A preferred arrangement for lifting the filter bell l2 from its seat on the flange comprises the columns l9, which pass through aligned holes 34 in the flanges I1 and I8, the cross member 20, the threaded shaft 2| and the hand wheel 23.

The columns l3 are secured at their lower ends to the under surface of the flange I! by the nuts 24, and at their upper ends to the cross member 20 by the nuts 25. The cross member 20 is drilled vertically at its centre and is tapped to receive, in threaded engagement, the threaded shaft 2|. The handwheel 23 is keyed to the upper end of the shaft 2| above the cross member 20. The lower end of the shaft is secured to the upper end of the filter bell by a conventional lifting arrangement, such as by a collar or ring 26 which is fitted into a groove cut into a projection or boss 21 extending upwardly from the centre of the surface of the filter bell and into another groove or slot formed in the lower end of the shaft. The filter bell is raised from and lowered to its seat on the flange I! by turning the handwheel 23, the columns |9 serving as guides to hold the bell in alignment with its position on the seat.

When the filtering apparatus is assembled, the filter bell is firmly secured to the filtrate receiving basin by the eye-bolts 31 which pass through aligned slots 39 in the flanges l1 and I8 and are secured in their "fixed position by the nuts 38.

The filter bell is provided with an inlet pipe 28 extending from a holding pot 4| to the upper part of the filter bell. An air pipe 3| extends from an air compressor 43 to the inlet pipe 28.

An outlet pipe 29 extends from the lower part of the filter bell to the holding pot. Each of the inlet and outlet pipes 28 and 29 is provided with a valve 32 and 33 respectively, to regulate the fiow of metal therethrough.

The operation of the apparatus is described hereinafter as applied to the filtration of molten iron-bearing tin in which the iron content is in the form of solid particles of iron-tin compound suspended in and dispersed throughout the molten tin. The filter is first heated to prevent solidification of the tin passed thereinto. In heating, care must be taken to avoid raising the temperature of the filter to a temperature at which the iron-tin compound would be soluble in the tin to any appreciable extent. In normal operations, the molten iron-bearing tin is stored in the holding pot at a temperature above 232 C., the melting temperature of the tin, and preferably below 400 C. It is found that by circulating the tin from the holding pot through the filter bell I2 and thence back to the holding pot, the filter bell is heated to the desired operating temperature without any danger of overheating.

The apparatus is first assembled and all conmotions are made secure. The filter is then heated by circulating, by means of pump 42,

4 molten tin from the holding pot through pipe 28, through the filter bell l2 and out the outlet pipe 23 for return to the holding pot, the valves 32 and 33 beingopen to permit the unrestricted flow through those pipes. A certain minor amount of solidification of the crude tin may take place in the cover during the preliminary heating .stages but this is quickly re-melted by the continuous flow of the hot metal. The resistance of the filtering medium I0 is suflicient to prevent the fiow therethrough of appreciable amounts of molten metal while the valve 33 remains open.

When the filter has been heated to the desired temperature, the valve 33 in pipe 29 is closed and the molten tin passed into the filter is forced through the filtering medium ID, the filtrate being received in the filtrate receiving basin H from which it flows, by gravity, through the pipe l5 to a casting pot. After all the tin in the holding pot has been passed through the filter, the valve 35 in air pipe 3| is opened and compressed air is forced into and through pipe 28. The portion of the pipe 28 between air pipe 3| and the holding pot is first cleared by blowing that line free of tin to prevent solidification of tin therein. The valve 32 is then closed to increase the pressure on the filter cake which collected on the filtering medium during the filtering operation. The molten tin retained in the filter cake is forced through the cake and through the filter cloth into the filtrate receiving basin and then to the casting pot. When no more tin can be extracted from the cake by the pressure of the compressed air, the air is turned off and the air and metal inlet and outlet pipes to the filter hell are disconnected. The filter bell may then be raised on columns I9 by turning handwheel 23 to permit removal of the filter cake.

Ordinarily, the filtering apparatus is constructed of iron or steel. Metals which are soluble in tin, such as lead and copper, should not be used in parts which are contacted by the tin.

The preferred filtering medium is asbestos cloth. Satisfactory results have been obtained from the use of other filtering media such as cotton waste, blanket wool, felt, glass cloth, asbestos shreds, and asbestos powder. Asbestos cloth is preferred, however, as it is easily handled and provides a filtering medium which is of substantially uniform density. The periphery of the asbestos cloth also serves as a gasket to seal the joint between the flanges of the filter bell and the filtrate receiving basin.

The amount of crude tin that can be filtered without interrupting the filtering operation depends upon the capacity of the filter bell and upon the iron content of the metal. If the iron content is high, of course, the filter bell can be designed to accommodate the increased amount of filter cake which will be formed.

It has been found that a satisfactory rate of filtering may be obtained when the metal'from the holding pot is Dumped into the filter bell under a pressure of from 15 to 30 pounds per square inch. Under the described conditions, a rate of filtration of about 4.5 pounds of metal per minute per square inch of filtering surface has been obtained.

Exemplifying the operation of the present method and apparatus, the iron content of the crude tin undergoing treatment is usually from 0.04% to 0.4% Fe, although tin containing as much as 6% iron has been successfully treated, the iron content being reduced to less than 0.007% Fe. Tin metal containing as little as method and the iron content reduced to about 0.006% Fe. A reduction to 0.001% Fe has been obtained in'some cases.v

Filter cake from the treatment of the crude city of the filter bell, which contingency would normally be taken into consideration when designing the filter; or unless it exceeds much more than 6%, in which case the fluidity of the metal quantities as to form a cake exceeding the capais so reduced that pumping and filtering become tin is found to contain from 10% to Fe, that difficult. is, from 52% to 80% FeSn-r. The ironcontent of The recovery of marketable tin from the crude a-fiiter cake 100% FeSnr would be approximately product is of the order of 90% and higher. For 19% Fe. example, a crude tin containing 0.5% iron may be In the operation of the apparatus, the upper 0 filtered under the described conditions to produce temperature limit for filtration depends,upon marketable metal containing less than 0.01% the permissible iron content of the final product. iron, and a filter cake containing, for example, It has been found, however, that filtering at tem- 10% iron. As almost all the iron is removed from peratures of about 425 C. and higher will not the tin, a ton of crude metal would form a filter product consistently tin containing less than 15 cake weighing about 100 pounds and including 10 0.01% iron. Therefore, to produce tin containing pounds of iron. The recovery of marketable tin, consistently less than 0.01% iron, it is necessary therefore, would be of the order of about 95% to conduct the filtering operation at less than. of the ori inal iron-bearing metal. Loss of metal 425 C., for example about 400 C. or lower. It by oxidation is, of course, avoided in the present would follow that it would be preferable to oper- 2o process. 7 ate within a temperature range closely approxi- The treatment herein is equally applicable to mating 232 0., the melting point of tin, as for reduce the iron content of refined tin or what example, 232 C. to 250 C. However, operating is known as 'Standard'f tin. Standard" tin at a temperature so close to the melting point .must contain at least 99.75% tin. The che l m of tin presents practical dificulties in temperacomposition of pig tin must be in accordance ture control and in manipulation of the metal. with the following table if it is to meet with It has been found that highly satisfactory operat- United States, G vernment requirements:

(13in) (122:) (152:) Cd (fizz) (133:) (13:) (1 1:) of) A Epercent; 99.75 0.10 0.10 None None 0.10 0.10 0.01 0.01 0.01 B percent 98.00 1.50 1.50 None None 0.10 0.10 0.10 0.10 0.01

ing results are obtained at temperatures between Tin from various sources, such as from the 250 C. and 400 0., preferably at about 350'C., Netherlands East Indies, may come well within the iron content of the resulting tin being less the United States Government specifications for than 0.01%, and, at the same time, difficulties in grade A tin except for its iron content. This temperature control and in manipulation of the iron content can be quickly and inexpensively metal are avoided. 1 40 reduced by the present apparatus to between While the apparatus has been described as 0.001% and 0.006%, and the tin thus brought up being applied to the separation and removal of to gradeAspecificatiOn W the'iron content from iron-bearing crude or re- .It will be understood/that modifications from fined tin, it is applicable to the separation and the preferred embodiment of the invention deremoval of solld impurities from other molten scribed and illustrated herein may be made by metals, particularly metals having a relatively others skilled in the art in the light of the teachlow melting temperature such as lead, tin, and ings herein. lead-tin alloy The pparatus is particularly What we claim as new and desire to protect effective forseparating and removing the iron by Letters Patent of the United States is: content from an iron-bearing crude and refin d 1. Apparatus for filtering tin which comprises tin. The presence of iron in tin and its removal I a filtrate receiving basin, an outlet forsaid basin, has con tituted a diflicult P b m in the art (1118 a cover for said basin detachably securable thereto the dispersal of the ironthroughout the molten t in substantially air-sealing engagement, fllbath as solid crystalline particles of iron-tin comt l medmm between m cover and said basin, Pound of y slightly reat r Sp c gr y aninlet conduit to said cover in communication than the specific gravity of the molten tin in t a source of supply of molten tin and with which t y e dispersed consequently, it a source of supply of air under pressure, an outhas not been possible heretofore to separate efiect u; from said cover in communication tively, and substantially completely the iron-tin t t source of supply of molten gm 4 particles from the molten tin without attendant to conduits extending into said cover above said wasteful 105585 of the metal filtering medium and the inlet end of the out- The advantages of the use of the pres nt app let conduit being positioned adjacent to the filratus for the substantially complete removal of g m; medium valves v said conduits for reghe p y n from the l @111 Over the ulating the flow of molten tin and air to said Eq i boiling and 9 1mg methods of the prior cover and molten tin from said cover, said inlet a t are s i t The equipment required s and outlet conduits being adapted-to circulate inexpensive and is easily constructed of readily lt tin from d t th u supply available material. The time of treatment is through all parts of said cover and the valve in greatlyreduced in that a lot of ten tons of crude the outlet conduit being adapted to stop such tin can be filtered in less than half an hour circulation, pressure means for maintaining said using a filter having a filtering surface only 16 circulation and for forcing molten tin through inches in diameter. The amount of iron in the said filtering medium when said circulation is crude tin has little eflect on the rate of flltrastopped, means for forcing through the filtering ticn unless, of course, it is present in such large medium the molten tin contained in the residue retained thereon, and means for raising the cover for removal of the residue collected on the filtering medium.

2. Apparatus for filtering tin which comprises a filtrate receiving basin, an outlet for said basin,

let conduit from said cover in communication with the source of supply of molten tin, said conduits extending into said cover above said filtering medium and the inlet end of the outlet conduit being positioned adjacent to the filtering medium, valves in said conduits for regulating the flow of molten tin and air to said cover and molten tin from said cover, said inlet and outlet conduits being adapted to circulate molten tin from and to the source of supply through all 'parts of said cover and the valve in the outlet conduit being adapted to stop such circulation, pressure means for maintaining said circulation and for forcing molten tin through said filtering medium when said circulation is stopped, means for forcing through the filtering medium the molten tin contained in the residue-detained thereon, and means for raising the cover in alignment with the basin for removal of the residue collected on the filtering medium.

3. Apparatus for filtering tin which comprises a filtrate receiving basin having a flanged upper rim, an outlet for said basin, a vertically disposed frame having side members and a transverse member above said basin, a bell shaped cover having a flanged lower rim, means for raising and lowering 'said cover in said frame out of and into engagement with said basin, mean for detachably securing the cover and basin together in substantially air sealing engagement with a filtering medium therebetween, an inlet conduit to said cover in communication with a source of supply of molten tin and with a source of air under pressure, an outlet conduit from said cover in communication with the source of supply of molten tin, said conduits extending into said cover above aid filtering medium and the inlet end of the outlet conduit being positioned adjacent to the filtering medium, valves in said conduits for regulating the flow of molten tin and air to said cover and molten tin from said cover, said inlet and outlet conduits being adapted to circulate molten tin from and to the source of supply through all parts or said cover and the valve in the outlet conduit being adapted to stop such circulation, pressure means for maintaining said circulation and for forcing molten tin through said filtering medium when the circulation is stopped, and means for forcing through the filtering medium the molten tin contained in the residue retained thereon.

ROBERT LEPSOE.

EDWARD LLEWELYN JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 776,222 Derham Nov. 29, 1904 1,181,729 Brown May 2, 1916 1,567,990 Apablasa Dec. 29, 1925 1,656,200 Homing Jan. 17, 1928 1,710,398 Bakken Apr. 23, 1929 1,749,730 Kenney Mar. 4, 1930 1,820,141 Jessup Aug. 25, 1931 1,948,479 Caminez Feb, 20, 1934 1,988,227 Wirth Jan. 15, 1935 1,995,593 Wefelscheid Mar. 26, 1935 2,063,742 Holmes Dec. 8, 1936 2,068,395 Burckhalter Jan. 19, 1937 2,106,863 Whitney Feb. 1, 1938 2,214,671 Hagan Sept. 10, 1940 2,335,365 Smith Nov. 30, 1943 FOREIGN PATENTS Number Country Date 16,987 Great Britain Dec. 29, 1884 France July 10, 1928 

